Enforce the timing cpu ticking at it's clock rate

Enforce the timing cpu ticking at it's clock rate
Add a max time option in seconds and a single system root clock be 1THz

configs/test/fs.py:
    Add a max time option in seconds and a single system root clock be 1THz
src/cpu/simple/timing.cc:
src/cpu/simple/timing.hh:
    Enforce the timing cpu ticking at it's clock rate

--HG--
extra : convert_revision : a1b0de27abde867f9c3da5bec11639e3d82a95f5